After 422 Million Miles, Phoenix Touches Down

Mars was a big news-maker last week, with the successful landing on Sunday of the Phoenix Mars Lander. The probe performed perfectly, which was a relief in the wake of the 1999 disappearance of the Mars Polar Lander.

Earlier in the week, scientists reported that radar imaging from NASA's Mars Reconnaissance Orbiter spacecraft detected as many as seven layers of ice and dust under the planet's north pole. Phoenix will dig down into the polar soil to determine what's there. Elsewhere on the planet, the Mars rover Spirit uncovered evidence of ancient hot springs, a discovery with possible implications for life.

In other space news, astronomers said they were just plain lucky to witness the beginning of a supernova, the fiery death of a star. It was detected by a NASA X-ray satellite while observing another, more advanced supernova.

And astrophysicists reported that much of the missing matter in the universe appears to be clustered in the space between galaxies in a vast web-like structure. But they say they cannot fully account for the majority of normal matter believed to have been created by the big bang.

Ten years ago this month the Astronomical Journal accepted a paper for publication that revealed a dark side to gravity. So-called "dark energy," a force that repels gravity, has become the most profound problem in physics, according to National Geographic.